A system of this type which does not belong to the microwave domain is described in British Patent Specification 1 532 753. In this prior-art system data organized as binary words are transmitted accompanied by a parity code over a first transmission channel and supplementary data of the same binary words having binary elements of opposite value are transmitted over the auxiliary channel. The comparison on reception of the binary elements coming from transmission channels and auxiliary channels makes it possible to rapidly detect a transmission error.